The disclosure relates to gas turbine engines. More particularly, the disclosure relates to hot-corrosion resistant bondcoats for thermal barrier coatings for gas turbine engines.
Gas turbine engine gaspath components are exposed to extreme heat and thermal gradients during various phases of engine operation. Thermal-mechanical stresses and resulting fatigue contribute to component failure. Significant efforts are made to cool such components and provide thermal barrier coatings to improve durability.
Exemplary thermal barrier coating systems include two-layer thermal barrier coating systems. An exemplary system includes NiCoCrAlY bondcoat as the first layer (e.g., low pressure plasma sprayed (LPPS)) and yttria-stabilized zirconia (YSZ) (or gadolinia-stabilized zirconia (GSZ)) thermal barrier coating (TBC) (e.g., air plasma sprayed (APS), suspension plasma sprayed (SPS) or electron beam physical vapor deposited (EBPVD)) as the second layer. Prior to and while the thermal barrier coat layer is being deposited, a thermally grown oxide (TGO) layer (e.g., alumina) forms atop the bondcoat layer. As time-at-temperature and the number of cycles increase during subsequent service exposure, this TGO interface layer grows in thickness. An exemplary YSZ is 7 weight percent yttria-stabilized zirconia (7YSZ).
Exemplary TBCs are applied to thicknesses of 1-40 mils (0.025-1.0 mm) and can contribute to a temperature reduction of up to 300° F. (167° C.) at the base metal. This temperature reduction translates into improved part durability, or higher turbine operating temperatures and improved turbine efficiency.